Cobalt extraction method

ABSTRACT

The objective of the present invention is to selectively extract cobalt from an acidic solution containing a high concentration of manganese. This cobalt extraction method extracts cobalt from an acidic solution containing manganese and cobalt by subjecting the acidic solution to solvent extraction by means of a valuable metal extraction agent comprising an amide derivative represented by general formula (I). The valuable metal extraction agent is represented by the general formula. In the formula: R 1  and R 2  each represent the same or different alkyl group; R 3  represents a hydrogen atom or an alkyl group; and R 4  represents a hydrogen atom or any given group aside from an amino group bonded to the α carbon as an amino acid. Preferably, the general formula has a glycine unit, a histidine unit, a lysine unit, an aspartic acid unit, or an N-methylglycine unit. Preferably, the pH of the acidic solution is 3.5-5.5 inclusive.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP2012/078446, filed Nov. 2, 2012,which claims the benefit of Japanese Patent Application No. 2012-225454,filed Oct. 10, 2012; Japanese Patent Application No. 2012-178293, filedAug. 10, 2012; Japanese Patent Application No. 2012-056143, filed Mar.13, 2012; and Japanese Patent Application No. 2011-245981, filed Nov. 9,2011, the entire contents of the aforementioned applications are herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a cobalt extraction method.

BACKGROUND ART

Cobalt and rare earth metals are known as valuable metals and used forvarious applications in industry. Cobalt is used for positive electrodematerials for secondary batteries, and, furthermore, superalloys (highstrength heat-resistant alloys) used for e.g. jet engines for aircraft,and the like. Rare earth metals are used for fluorescent materials,negative electrode materials for nickel-hydrogen batteries, additivesfor magnets installed in motors, abrasives for glass substrates used forliquid crystal display panels and hard disk drives, and the like.

In recent years, energy savings have been strongly promoted, and in theautomobile industry, conventional gasoline-engined cars are beingrapidly replaced by hybrid cars and electric cars equipped withsecondary batteries using cobalt and rare earth metals. In lightingequipment, conventional fluorescent lamps are being rapidly replaced byefficient three band fluorescent lamps using rare earth metals such aslanthan, cerium, yttrium, terbium and europium. The above cobalt andrare earth metals are scarce resources, and most of them depend onimports.

Yttrium and europium have been used for fluorescent substances incathode ray tube television sets in analog broadcasting; however, inrecent years, large numbers of cathode ray tubes have been put out ofuse because of the transition to liquid crystal television sets.Products which have rapidly spread, such as secondary batteries andthree band fluorescent lamps, can be also easily expected to cause alarge amount of waste in the future as used products. Thus, cobalt andrare earth metals, scarce resources, are treated as waste withoutrecycling of the used products, which is not preferred in terms ofresource savings and resource security. Nowadays, the establishment of amethod for effectively retrieving valuable metals such as cobalt andrare earth metals from such used products is strongly demanded.Retrieval of cobalt from secondary batteries

The above secondary batteries, incidentally, include nickel-hydrogenbatteries, lithium ion batteries and the like, and in addition tocobalt, a rare earth metal, manganese is used for positive electrodematerials thereof. In positive electrode materials in lithium ionbatteries, the ratio of low cost manganese tends to be increased inplace of high cost cobalt. The retrieval of valuable metals from usedbatteries has been attempted recently, and as one of the retrievalmethods, there is a dry method in which used batteries are thrown into afurnace and melted, and metals and slag are separated to retrieve themetals. In this method, however, manganese moves to slag, and thus themetal that can be retrieved is only cobalt.

Further, a wet method is known, in which used batteries are dissolved inan acid and metals are retrieved using a separation method such as aprecipitation method, a solvent extraction method or an electrowinningmethod. In the precipitation method, for example, a method in which thepH of a solution comprising cobalt and manganese is adjusted and asulphurizing agent is added thereto to obtain a cobalt sulphideprecipitate, and a method in which an oxidizing agent is added theretoto obtain a manganese oxide precipitate are known (see Patent Document1). The methods, however, have problems such as the occurrence ofcoprecipitation, and it is difficult to completely separate cobalt andmanganese.

It is known that when cobalt is retrieved as a metal by theelectrowinning method, in a system in which a high concentration ofmanganese exists, manganese oxides are precipitated on the surface of ananode and deterioration of the anode is promoted. In addition, apeculiar colored fine manganese oxide is suspended in an electrolyticsolution, and thus, for example, clogging of the filter cloth used forelectrowinning and contamination of cobalt metal by the manganese oxideoccur. Therefore, stable operations are difficult.

When cobalt is retrieved using the solvent extraction method, an acidextraction agent is widely used. As described above, however, nowadaysmanganese is used in large amounts for positive electrode materials inlithium ion batteries, and thus a high concentration of manganese existsin the solution in the batteries. Efficient extraction agents whichselectively and efficiently extract cobalt from such a system do notexist in the existing circumstances.

In addition to recycling used batteries, in cobalt smelting which iscurrently carried out to produce cobalt, a raw material is a nickel oresuch as a nickel oxide ore. The percentage of manganese is howeverhigher than that of cobalt in the nickel oxide ore, and the existingpercentage thereof is about 5 to 10 times that of cobalt. When cobalt issmelted, separation from manganese is a major problem.

-   Patent Document 1: Japanese Unexamined Patent Application,    Publication No. 2000-234130-   Non-Patent Document 1: K. Shimojo, H. Naganawa, J. Nora, F. Kubota    and M. Coto; Extraction behavior and separation of lanthanides with    a diglycol amic acid derivative and a nitrogen-donor ligand; Anal.    Sci., 23, 1427-30, 2007 December.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a method forselectively extracting cobalt from an acid solution comprising a highconcentration of manganese.

As a result of repeated intensive investigation to solve the aboveproblem, the present inventors found that the above object could beachieved by using a valuable metal extraction agent comprising an amidederivative represented by the following general formula (I), completingthe present invention.

Means for Solving the Problems

Specifically, the present invention provides as follows.

(1) The present invention is a cobalt extraction method, wherein an acidsolution containing manganese and cobalt is subjected to solventextraction by a valuable metal extraction agent comprising an amidederivative represented by the following general formula (I) to extractthe cobalt from the acid solution:

(wherein, R¹ and R² each represent the same or different alkyl groups;the alkyl group can be a straight chain or a branched chain; R³represents a hydrogen atom or an alkyl group; and R⁴ represents ahydrogen atom or any group other than an amino group, which is bound tothe α carbon as an amino acid).

(2) The present invention is also the cobalt extraction method accordingto (1), wherein the amide derivative is any one or more of glycinamidederivatives, histidinamide derivatives, lysinamide derivatives, asparticacid amide derivatives and N-methylglycine derivatives.

(3) The present invention is also the cobalt extraction method accordingto (1) or (2), wherein the acid solution is subjected to the solventextraction with the pH of the acid solution adjusted to a range of 3.5or more to 5.5 or less.

Effects of the Invention

According to the present invention, cobalt can be selectively extractedfrom an acid solution comprising a high concentration of manganese.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figure showing a ¹H-NMR spectrum of a glycinamide derivativesynthesized in Example 1.

FIG. 2 is a figure showing a ¹³C-NMR spectrum of a glycinamidederivative synthesized in Example 1.

FIG. 3 shows the results of the extraction of cobalt from an acidsolution comprising cobalt and manganese using the valuable metalextraction agent of Example 1.

FIG. 4 shows the results of the extraction of cobalt from an acidsolution comprising cobalt and manganese using the valuable metalextraction agent of Example 2.

FIG. 5 shows the results of the extraction of cobalt from an acidsolution comprising cobalt and manganese using the valuable metalextraction agent of Example 3.

FIG. 6 shows the results of the extraction of cobalt from an acidsolution comprising cobalt and manganese using the valuable metalextraction agent of Comparative Example 1.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

The specific embodiments of the present invention will now be describedin detail. It should be noted, however, that the present invention isnot restricted to the following embodiments and can be carried out withproper modification within the scope of the object of the presentinvention. Cobalt extraction method

In the cobalt extraction method of the present invention, cobalt isextracted from an acid solution by solvent extraction by a valuablemetal extraction agent comprising an amide derivative represented by thefollowing general formula (I).

In the formula, substituents R¹ and R² each represent the same ordifferent alkyl groups. The alkyl group can be a straight chain or abranched chain. R³ represents a hydrogen atom or an alkyl group. R⁴represents a hydrogen atom or any group other than an amino group, whichis bound to the α carbon as an amino acid. In the present invention,lipophilicity is increased by introducing alkyl groups into the amideskeleton, and the compound can be used as an extraction agent.

The above amide derivative is any one or more of glycinamidederivatives, histidinamide derivatives, lysinamide derivatives, asparticacid amide derivatives and N-methylglycine derivatives. When the amidederivative is a glycinamide derivative, the above glycinamide derivativecan be synthesized by the following method. First, a 2-halogenatedacetyl halide is added to an alkylamine having a structure representedby NHR¹R² (R¹ and R² are the same as the above substituents R¹ and R²),and the hydrogen atom of amine is substituted with a 2-halogenatedacetyl by the nucleophilic substitution reaction to obtain a2-halogenated (N,N-di)alkylacetamide.

Next, the above 2-halogenated (N,N-di)alkylacetamide is added to glycineor an N-alkylglycine derivative, and one of the hydrogen atoms of theglycine or N-alkylglycine derivative is substituted with an(N,N-di)alkylacetamide group by the nucleophilic substitution reaction.A glycine alkylamide derivative can be synthesized by the two-stepreactions.

A histidinamide derivative, a lysinamide derivative or an aspartic acidamide derivative can be synthesized by substituting glycine withhistidine, lysine or aspartic acid. The extraction behavior of lysineand aspartic acid derivatives is, however, thought to be within therange of the results obtained by using a glycine derivative and ahistidinamide derivative according to the complex stability constant ofmanganese, cobalt and the like, which are targets.

To extract valuable metal ions using an extraction agent synthesized bythe above method, with an acid aqueous solution comprising the objectivevaluable metal ions being adjusted, the acid aqueous solution is addedto an organic solution of the above extraction agent, and mixed.Therefore, the objective valuable metal ions can be selectivelyextracted in the organic phase.

The organic solvent after extraction of the valuable metal ions iscollected, and to this, a starting solution for back extraction is addedand stirred to separate the objective valuable metal ions by extractionto an organic solvent, which starting solution is adjusted to a pH lowerthan that of the above acid aqueous solution. The objective valuablemetal ions can be further retrieved from the organic solvent in anaqueous solution by back extraction of the objective valuable metalions. As a solution for back extraction, for example, an aqueoussolution in which nitric acid, hydrochloric acid or sulfuric acid isdiluted is suitably used. In addition, the objective valuable metal ionscan be concentrated by suitably changing the ratio of the organic phaseand the aqueous phase.

Any organic solvent can be used, as long as an extraction agent and theextracted species of metals are dissolved with the solvent, and examplesthereof include chlorine-based solvents such as chloroform anddichloromethane, aromatic hydrocarbons such as benzene, toluene andxylene, aliphatic hydrocarbons such as hexane, and the like. Theseorganic solvents can be used individually, or two or more organicsolvents can be mixed, and alcohols such as 1-octanol can be mixedtherewith.

The concentration of the extraction agent can be properly set dependingon the types and concentrations of valuable metals. In addition, theequilibrium arrival time varies depending on the types andconcentrations of valuable metals and the amounts of extraction agent tobe added, and thus the stirring time and extraction temperature can besuitably set depending on the conditions of an acid aqueous solution ofvaluable metal ions and an organic solution of the extraction agent. ThepH of an acid aqueous solution comprising metal ions can be alsosuitably adjusted depending on the types of valuable metal.

Extraction of Cobalt

When cobalt is efficiently retrieved from an acid aqueous solutioncontaining cobalt and manganese, any amino derivative of the above aminoderivatives can be used as an extraction agent. Among these, it ispreferred to use an N-methylglycine derivative or a histidinamidederivative since the suitable pH range is wide and thus the convenienceis greater when cobalt is industrially extracted. Regarding pH, it ispreferred that, with the pH of an acid aqueous solution comprisingcobalt and manganese adjusted to 3.5 or more and 5.5 or less, an organicsolution of an extraction agent be added thereto, and it is morepreferred that, with the above pH adjusted to 4.0 or more and 5.0 orless, an organic solution of an extraction agent be added thereto. Whenthe pH is less than 3.5, there is a possibility that cobalt cannot besufficiently extracted depending on the types of extraction agent. Whenthe pH is above 5.5, there is a possibility that not only cobalt butalso manganese is extracted depending on the types of extraction agent.

The mechanism in which the extraction agent of the present invention hasan extraction behavior different from conventional extraction agents isnot accurately grasped, and it is thought that the effects whichconventional extraction agents do not have are obtained by thestructural characteristics of the extraction agent of the presentinvention.

EXAMPLES

The present invention will now be described in more detail by way ofexamples. It should be noted, however, that the present invention is notrestricted to these descriptions.

Example 1 Synthesis of Glycinamide Derivatives

As an example of amide derivatives forming an extraction agent, aglycinamide derivative represented by the following general formula (I)was synthesized, that is,N—[N,N-bis(2-ethylhexyl)aminocarbonylmethyl]glycine (or also referred toas N,N-di(2-ethylhexyl)acetamide-2-glycine), hereinafter referred to as“D2EHAG”), into which two 2-ethylhexyl groups are introduced.

D2EHAG was synthesized as follows. First, as shown in the followingreaction formula (II), 23.1 g (0.1 mol) of commercially availabledi(2-ethylhexyl)amine and 10.1 g (0.1 mol) of triethylamine werecollected. These were dissolved by adding chloroform, and 13.5 g (0.12mol) of 2-chloroacetyl chloride was then added by drops thereto,followed by washing with 1 mol/1 hydrochloric acid once. After this,washing was carried out with ion exchanged water and the chloroformphase was collected.

Next, anhydrous sodium sulphate was added in a suitable amount(approximately 10 to 20 g) for dehydration, followed by filtration toobtain 29.1 g of yellow liquid. When the structure of this yellow liquid(reaction product) was identified using a nuclear magnetic resonancespectrometer (NMR), the above yellow liquid was confirmed to have thestructure of 2-chloro-N,N-di(2-ethylhexyl)acetamide (hereinafterreferred to as “CDEHAA”). The percent yield of CDEHAA was 90% relativeto di(2-ethylhexyl)amine, a raw material.

Next, as shown in the following reaction formula (III), 8.0 g (0.2 mol)of sodium hydroxide was dissolved by adding methanol, and 15.01 g (0.2mol) of glycine was further added thereto. While stirring the obtainedsolution, 12.72 g (0.04 mol) of the above CDEHAA was slowly added bydrops thereto and stirred. After completion of stirring, the solvent inthe reaction liquid was distilled off, and the residue was dissolved byadding chloroform. To this solution, 1 mol/1 sulphuric acid was addedfor acidification, followed by washing with ion exchanged water, and thechloroform phase was collected.

To this chloroform phase, anhydrous magnesium sulphate was added in asuitable amount for dehydration, followed by filtration. The solvent wasremoved under reduced pressure again to obtain 12.5 g of yellow paste.The percent yield based on the amount of the above CDEHAA was 87%. Whenthe structure of the yellow paste was identified by NMR and elementalanalysis, the paste was confirmed to have the structure of D2EHAG asshown in FIG. 1 and FIG. 2. The above steps were carried out to obtain avaluable metal extraction agent of Example 1.

Example 2 Synthesis of N-methylglycine Derivatives

As another example of amide derivatives forming an extraction agent, anN-methylglycine derivative represented by the following general formula(I) was synthesized, that is,N-[N,N-bis(2-ethylhexyl)aminocarbonylmethyl]sarcosine (or also referredto as N,N-di(2-ethylhexyl)acetamide-2-sarcosine), hereinafter referredto as “D2EHAS”), into which two 2-ethylhexyl groups are introduced.

D2EHAS was synthesized as follows. As shown in the following reactionformula (IV), 5.3 g (0.132 mol) of sodium hydroxide was dissolved byadding methanol, and 11.8 g (0.132 mol) of sarcosine (N-methylglycine)was also added thereto. While stirring the obtained solution, 36.3 g(0.12 mol) of the above CDEHAA was slowly added by drops thereto andstirred. After completion of stirring, the solvent in the reactionliquid was distilled off, and the residue was dissolved by addingchloroform. To this solution, 1 mol/1 sulphuric acid was added foracidification, followed by washing with ion exchanged water, and thechloroform phase was collected.

To this chloroform phase, anhydrous magnesium sulphate was added in asuitable amount for dehydration, followed by filtration. The solvent wasremoved under reduced pressure again to obtain 26.8 g of yellowish brownpaste. The percent yield based on the amount of the above CDEHAA was60%. When the structure of the yellow paste was identified by NMR andelemental analysis, the paste was confirmed to have the structure ofD2EHAS. The above steps were carried out to obtain a valuable metalextraction agent of Example 2.

Example 3 Synthesis of Histidinamide Derivatives

As another example of amide derivatives forming an extraction agent, ahistidinamide derivative represented by the following general formula(I) was synthesized, that is,N-[N,N-bis(2-ethylhexyl)aminocarbonylmethyl]histidine (or also referredto as N,N-di(2-ethylhexyl)acetamide-2-histidine), hereinafter referredto as “D2EHAH”), into which two 2-ethylhexyl groups are introduced.

D2EHAH was synthesized as follows. As shown in the following reactionformula (V), 16 g (0.4 mol) of sodium hydroxide was dissolved by addingmethanol, and 31.0 g (0.2 mol) of histidine was also added thereto.While stirring the obtained solution, 13.2 g (0.04 mol) of the aboveCDEHAA was slowly added by drops thereto. After completion of thedrop-by-drop addition, stirring was carried out with alkaline conditionsmaintained. After completion of stirring, the solvent in the reactionliquid was distilled off, and the residue was dissolved by adding ethylacetate. This solution was washed, and the ethyl acetate phase wascollected.

To this ethyl acetate phase, anhydrous magnesium sulphate was added in asuitable amount for dehydration, followed by filtration. The solvent wasremoved under reduced pressure again to obtain 9.9 g of yellowish brownpaste. The percent yield based on the amount of the above CDEHAA was57%. When the structure of the yellowish brown paste was identified byNMR and elemental analysis, the paste was confirmed to have thestructure of D2EHAH. The above steps were carried out to obtain avaluable metal extraction agent of Example 3.

Comparative Example 1

As a valuable metal extraction agent of Comparative Example 1, acommercially available carboxylic acid-based cobalt extraction agent(Product name: VA-10, neodecanoic acid, manufactured by Hexion SpecialtyChemicals Japan) was used.

Comparative Example 2

As a valuable metal extraction agent of Comparative Example 2,N,N-dioctyl-3-oxapentan-1,5-amic acid (hereinafter referred to as“DODGAA”), a conventionally known europium extraction agent was used.

DODGAA was synthesized as follows. First, as shown in the followingreaction formula (VI), 4.2 g of anhydrous diglycolic acid was put into around bottom flask, and 40 ml of dichloromethane was put therein andsuspended. After that, 7 g of dioctylamine (purity 98%) was dissolved in10 ml of dichloromethane, and the obtained solution was slowly addedthereto using a dropping funnel. While stirring the solution at roomtemperature, the solution was confirmed to become clear by the reactionof anhydrous diglycolic acid, and the reaction was completed.

Subsequently, the above solution was washed with water to removewater-soluble impurities. After washing with water, sodium sulphate wasadded to the solution as a dehydrating agent. The solution was subjectedto suction filtration, and the solvent was then vaporized.Recrystallization was carried out with hexane (three times), followed byvacuum drying. The yield of the obtained substance was 9.57 g, and thepercent yield based on the above anhydrous diglycolic acid was 94.3%.When the structure of the obtained substance was identified by NMR andelemental analysis, the substance was confirmed to be DODGAA with apurity of 99% or more.

Extraction of Cobalt

Cobalt was extracted and separated using the valuable metal extractionagents of Examples 1 to 3 and Comparative Example 1.

Examples 1 to 3

Several types of acid solution of sulphuric acid comprising cobalt andmanganese each in an amount of 1×10⁻⁴ mol/l and being adjusted to pH 2.5to 7.5, and an equal volume of an n-dodecane solution comprising 0.01mol/l of a valuable metal extraction agent were added together in testtubes, and the test tubes were put into a constant temperature oven at25° C. and shaken for 24 hours. At this time, the pH of the sulphuricacid solution was adjusted using 0.1 mol/l sulphuric acid, ammoniumsulphate and ammonia.

After shaking, the aqueous phase was collected, and the cobaltconcentration and the manganese concentration were measured usinginductively coupled plasma-atomic emission spectroscopy (ICP-AES). Theorganic phase was subjected to back extraction using 1 mol/l sulphuricacid. The cobalt concentration and the manganese concentration in theback extraction phase were measured using ICP-AES. From thesemeasurement results, the extraction rates of cobalt and manganese weredefined as the amount of material in the organic phase/(the amount ofmaterial in the organic phase+the amount of material in the aqueousphase) and measured. The results of the use of the valuable metalextraction agent of Example 1 are shown in FIG. 3, the results of theuse of the valuable metal extraction agent of Example 2 are shown inFIG. 4, and the results of the use of the valuable metal extractionagent of Example 3 are shown in FIG. 5. In FIGS. 3 to 5, the abscissa isthe pH of an acid solution of sulphuric acid, and the ordinate is theextraction rate (unit: %) of cobalt or manganese. In the graphs, thesquare indicates the extraction rate of cobalt and the circle indicatesthe extraction rate of manganese.

Comparative Example 1

Cobalt was extracted by the same method as in the Examples except thatthe pH of an acid solution of sulphuric acid was adjusted to 4.0 to 7.5and the concentration of the n-dodecane solution comprising the valuablemetal extraction agent was changed to 0.1 mol/l, which is ten times theconcentration in the Examples. The results are shown in FIG. 6. In FIG.6, the abscissa is the pH of an acid solution of sulphuric acid, and theordinate is the extraction rate (unit: %) of cobalt or manganese. In thegraph, the square indicates the extraction rate of cobalt and thediamond indicates the extraction rate of manganese.

It was recognized that by using the valuable metal extraction agents ofthe Examples, cobalt could be extracted at an extraction rate of atleast above 20% in a pH range of 3.0 or more to 5.5 or less (FIG. 3 toFIG. 5). In particular, it was recognized that by using anN-methylglycine derivative or a histidinamide derivative, the suitablepH range was wide, and convenience was greater when industriallycarrying out the cobalt extraction of the present invention (FIG. 4,FIG. 5). It was also recognized that cobalt could be extracted at anextraction rate of above 80% and manganese was hardly extracted in a pHrange of 4.0 or more to 5.0 or less regardless of the types ofderivative (FIG. 3 to FIG. 5). Meanwhile, it was recognized that byusing the valuable metal extraction agent of Comparative Example 1,cobalt could be extracted only at an extraction rate of less than 20%even when the concentration of the extraction agent was ten times thatin the Examples (FIG. 6).

The invention claimed is:
 1. A cobalt extraction method, wherein an acidsolution containing manganese and cobalt is subjected to solventextraction by a valuable metal extraction agent comprising an amidederivative represented by general formula (I) to extract the cobalt fromthe acid solution:

wherein, R¹ and R² each represent the same or different alkyl groups;the alkyl group is optionally a straight chain or a branched chain; R³represents a hydrogen atom or an alkyl group; and R⁴ represents ahydrogen atom or any group other than an amino group, which is bound tothe α carbon as an amino acid.
 2. The cobalt extraction method accordingto claim 1, wherein the amide derivative is any one or more ofglycinamide derivatives, histidinamide derivatives, lysinamidederivatives, aspartic acid amide derivatives and N-methylglycinederivatives.
 3. The cobalt extraction method according to claim 1 or 2,wherein the acid solution is subjected to the solvent extraction withthe pH of the acid solution adjusted to a range of 3.5 to 5.5.
 4. Acobalt extraction agent comprising an amide derivative represented bygeneral formula (I):

wherein, R¹ and R² each represent the same or different alkyl groups;the alkyl group is optionally a straight chain or a branched chain; R³represents a hydrogen atom or an alkyl group; and R⁴ represents ahydrogen atom or any group other than an amino group, which is bound tothe α carbon as an amino acid.